Tetracyclines are used as broad spectrum antibiotics to treat various bacterial infections, such as infections of the respiratory tract, sinuses, middle ear, urinary tract, and intestines, and can be used in the treatment of gonorrhoea, especially in patients allergic to β-lactams and macrolides. Tetracyclines interfere with the protein synthesis of Gram positive and Gram-negative bacteria by preventing the binding of aminoacyl-tRNA to the ribosome. The action of tetracyclines is bacteriostatic (preventing growth of bacteria) rather than killing (bactericidal).
Tetracyclines degrade rapidly to form epitetracycline, anhydrotetracycline, epianhydrotetracycline, and other degradation products. Once degraded, tetracyclines have small therapeutic value, since the degradation products have no therapeutically useful activity. Degradation begins as soon as the antiobiotic is in solution, and continues until reaching an equilibrium of antibiotic and epimer concentrations. The equilibrium point is temperature and pH dependent, with more epimer being formed at higher temperatures and lower pH. Oxidation and other side reactions cause further degradation. Thus, tetracyclines can have a limited existence in aqueous environments in their active form. Moreover, the degradation products of tetracyclines are toxic and can cause Fanconi syndrome, a potentially fatal disease affecting proximal tubular function in the nephrons of the kidneys.
There is a need to provide hospital staff with the flexibility and advantages that come with longer admixture and reconstitution times without the need for refrigeration so that for instance, a hospital pharmacist could prepare a solution the day before it is needed. Furthermore, often after a natural disaster such as hurricanes, earthquakes, or tsunamis, access to refrigeration equipment can be scarce and may be further impeded by the lack of electricity. Stable formulations of tetracyclines could be stored as a solution, negating the need for reconstitution, and allowing its use in inhalers or nebulizers for outpatient use.
In addition, some tetracyclines can cause tetracycline-induced hemolysis. This hemolysis can lead to venous phlebitis at the site of injection when administered intravenously, resulting in irritation and potentially limiting the volumes of infusion that can be tolerated. Thus, there is a need for formulations of such tetracyclines that reduce the incidence of hemolysis.